Conduit boxes are used to attach electrical conduit to an exterior or interior surface of a building and to seal the wall penetrations while permitting access to the wiring.
These traditional conduit boxes are typically cast of aluminum or aluminum alloy. Such metals used will corrode from water exposure and have only limited impact resistance, with a tendency to crack. Being conductive, acid rain will react to accelerate corrosion of either the aluminum or the metallic fasteners used for attachment due to differences in contact potential.
In addition, rusting fastener screws accelerate oxidation and the rusting of aluminum or other metals.
Moreover, the joints between metal sill plates and plastic pipes joining to the metal conduit boxes are usually not in a water tight joint, since the materials don't fit together well.